Conventionally, an air-conditioner for a vehicle has an indoor unit equipped with a blower unit, a cooler unit, and a heater unit. Many blow-off ports are defined in the indoor unit of the air-conditioner, and air cooled or heated inside is blown off from the blow-off ports. Moreover, the indoor unit includes a ventilation control valve (hereafter referred as damper) which switches intake air between air outside a passenger compartment (hereafter referred as outside air) and air inside the passenger compartment (hereafter referred as inside air), an air mix damper which mixes cooled air and heated air with each other to air-condition, and a mode damper which adjusts the discharge amount of conditioned air blown off from each blow-off port. The damper may be called as a door.
Patent document 1 describes an electric actuator system in which an indoor unit includes an inside/outside air switch door, a driver seat side air mixing door, a passenger seat side air mixing door, and a blow-off mode switch door. Moreover, Patent document 1 discloses direct-current motors provided to respective doors, e.g., the inside/outside air switch door, the driver seat side air mixing door, the passenger seat side air mixing door, and the blow-off mode switch door, and a drive circuit which drives each direct-current motor.
A H-bridged circuit is known as such drive circuit for the direct-current motor in the air-conditioner. The H-bridged circuit for driving the direct-current motor has a circuit in which two switching elements are connected in series, and two of the circuits are disposed between a plus terminal and a minus terminal of a battery in parallel. A direct-current motor is disposed between connecting points at which the two switching elements are connected in the respective circuit. For example, Patent document 2 discloses a H-bridged circuit in which electric field effect type transistor is used as four switching elements. In Patent document 2, two of the transistors are on. A drive signal is input from a control circuit to gate of four electric field effect type transistors, and the two-on-transistors are switched among the four transistors, thereby changing the direction of current flowing through the direct-current motor so as to change the rotational direction of the direct-current motor.
However, in the air-conditioner shown in Patent document 1, if the H bridged circuit shown in Patent document 2 is used for driving four direct-current motors, e.g., the direct-current motor which drives the inside/outside air switch door, the direct-current motor which drives the driver seat side air mixing door, the direct-current motor which drives the passenger seat side air mixing door, and the direct-current motor which drives the blow-off mode switch door, four H bridged circuits are necessary and the circuit composition becomes complicated.